1. Field of Invention
The present invention relates to a surface acoustic wave (SAW) device. More particularly, the invention relates to a SAW device that includes a quartz plate and reduces frequency changes due to temperature variations, and to a method of adjusting a temperature characteristic.
2. Description of Related Art
Related art SAW devices include interdigital transducer (IDT) electrodes on the main surface of a piezoelectric plate represented by a piece of quartz so as to oscillate a high-frequency region in a stable manner. Among such SAW devices, in order to reduce frequency changes due to temperature variations, the related art also includes ST-cut SAW devices which include an ST-cut quartz plate as a piezoelectric plate, transmit SAW in the direction of the X-axis (the electrical axis) of the ST-cut quartz plate, and generate a Rayleigh wave, which is a kind of SAW.
In order to further reduce frequency changes due to temperature variations, a plurality of SAW elements are disposed on an ST-cut quartz plate in a manner that propagation directions of SAW generated by the SAW elements are different each other in one case, or in a manner that electrode thicknesses of IDT electrodes are different each other in another case, as disclosed in Japanese Unexamined Patent Application Publication No. 53-145595, for example.
Alternatively, an ST-cut quartz plate is rotated around the Z′-axis in an in-plane direction (hereinafter “in-plane rotation ST-cut quartz plate”). Then, a SAW element is disposed on the in-plane rotation ST-cut quartz plate (hereinafter “in-plane rotation ST-cut SAW device”), as disclosed in Japanese Examined Patent Application Publication No. 63-18892, for example.